|Authors: ||B. De Geyter, S. Abé, Z. Hens|
|Title: ||Postfocused Nanocrystal Diameter Tuning through Control of the Reaction Rate and the Solubility: Experiment vs. Realistic Modeling|
|Format: ||International Conference Poster|
|Publication date: ||12/2011|
|Journal/Conference/Book: ||MRS Fall Meeting 2011
|Editor/Publisher: ||Materials Research Society, |
|Location: ||Boston, United States|
|Citations: ||Look up on Google Scholar
We show that adjusting the reaction rate and solubility through ligand engineering in a hot injection synthesis is a viable strategy to tune the diameter of colloidal nanocrystals at the end of the size distribution focusing, i.e., the post-focused diameter. The approach is introduced by synthesis simulations, which describe nucleation and growth of colloidal nanocrystals from a solute or monomer that is formed in-situ out of the injected precursors. We present a coupled set of continuous rate equations, including monomer generation, nucleation and growth in one model. Instead of dimensionless parameters, we use common dimensions of diameter, time and concentration to keep comparison with experiments straightforward. We explore a three dimensional parameter space by adjusting the reaction rate for monomer generation, the solubility and the temperature.
These simulations indicate that the post-focused diameter is reached at almost full yield, and that it can be adjusted by the rate of monomer formation or the appropriate choice of ligand. We implement this size tuning strategy using a particular CdSe quantum dot synthesis that shows excellent agreement with the model synthesis. After demonstrating that the reaction rate depends in first order on the Cd and Se precursor concentration, the proposed strategy of size control is explored by varying the precursor concentration. This enables the synthesis of colloidal nanocrystals with a predefined size at almost full yield and sharp size distributions, which is highly relevant especially in the context of reaction upscaling and automation. Moreover, the results obtained challenge the traditional interpretation of the hot injection synthesis, in particular the link between hot injection, burst nucleation and sharp size distributions.